Growing season

Portion of the year in which local conditions permit normal plant growth

Geographic conditions have major impacts on the growing season for any given area. Latitude is one of the major factors in the length of the growing season. The further from the equator one goes, the angle of the Sun gets lower in the sky. Consequently, sunlight is less direct and the low angle of the Sun means that soil takes longer to warm during the spring months, so the growing season begins later. The other factor is altitude, with high elevations having cooler temperatures which shortens the growing season compared with a low-lying area of the same latitude.

The continental United States ranges from 49° north at the US-Canadian border to 25° north at the southern tip of the US-Mexican border. Most populated areas of Canada are below the 55th parallel. North of the 45th parallel, the growing season is generally 4–5 months, beginning in late April or early May and continuing to late September-early October, and is characterized by warm summers and cold winters with heavy snow. South of the 30th parallel, the growing season is year-round in many areas with hot summers and mild winters. Cool season crops such as peas, lettuce, and spinach are planted in fall or late winter, while warm season crops such as beans and corn are planted in late winter to early spring. In the desert Southwest, the growing season effectively runs in winter, from October to April as the summer months are characterized by extreme heat and arid conditions, making it inhospitable for plants not adapted to this environment.

Certain crops such as tomatoes and melons originated in subtropical or tropical regions. Consequently, they require hot weather and a growing season of eight months or more. In colder climate areas where they cannot be directly sowed in the ground, these plants are usually started indoors in a greenhouse and transplanted outside in late spring or early summer.

Northern Europe ranges from the 45th parallel up past the Arctic Circle. The growing seasons are shorter due to the lower angle of the Sun and generally range from five months to as little as three in Scandinavia and Russia. The Atlantic coast of Europe is moderated considerably by humid ocean air, thus winters are mild and it is rare to see freezing weather or snow. Summers are also mild and as a consequence, many heat-loving plants such as maize will not grow in northern Europe. Further inland, away from the ocean, winters become considerably colder. Despite the short growing season in Scandinavia and Russia, the extreme length of daylight during summer (17 hours or more) allows plants to put on significant growth.